Breadboard power reg.

Greeting all,

I am putting together a power regulator on my breadboard for a standalone Arduino to mock up my final circuit for a project.

I am using a LM7805 power regulator and after reviewing the schematic on this site i noticed it uses a 10uF and 1uF caps as apposed to a schematic i saw, and ordered parts for, on a different site that uses a 100uF and 10uF caps which brings me to the following questions.

(1) Is either configuration o.k..

(2) What difference does it make to the end circuit.

(3) Maybe a dumb question but can you go to high on the voltage ratting side, i think we all know what happens if you go to low... pop pop fiz fiz.

Thanks yet again for your time.

I'm no electrical engineer and don't exactly understand what they're for, but I overheard them talking about the caps.

Basically(I think) they're there to smooth out voltage "spikes" and make it more consistent.

Not sure how accurate that is, but my guess tell me that 10 and 100 would be best.

Basically(I think) they're there to smooth out voltage "spikes" and make it more consistent.

the smaller value of capacitor, the Higher frequency spikes it filters. the higher value of cap. the lower freq. spike it removes.

the smaller value of capacitor, the Higher frequency spikes it filters. the higher value of cap. the lower freq. spike it removes.

I have read about the purpose of the caps, that part is clear to me. I guess where i am lost is what is going on behind the curtain. How much play do i have with the cap sizes before i am not filtering a high and low enough frequency?

I'm fine with ordering some 1uF caps and sticking with the schematic on this site.... but it would be great to build on my limited knowledge base ;D.

Thanks for the responses.

How much play do i have with the cap sizes before i am not filtering a high and low enough frequency?

well it depends on where you're getting the power from, for example, from batteries you would hardly need to have any filtering because they have a pretty stable power output, but for rectified AC you'd need some higher frequency filtering

Rule of thumb: - If you are running noisy, junky DC into the input, use a big electrolytic ( 100Uf or more) and a small .1Uf on the input side. - For progressively cleaner power supplies, you can go down to 10Uf or so on the input side. The .1Uf should always be there, to ward off high frequency noise and spikes.

Longer answer: The big caps ( 10uf +) are there to smooth large variations of the DC input. The small caps are there to "short out" high frequencies that semiconductors don't like. A single noisy spike is a single cycle of high frequency energy, and the small cap will "quench" this.

There's a formula for this. It determines the reactance of the capacitor, which basically tells you how much resistance it will present to certain frequencies:

Xc= 1 / (2 x pi x frequency x capacitance)

if you run the numbers on this, you'll see that a .1Uf at 1Mhz is pretty much a short circuit: less than ten ohms. Conversely, at 10Hz it has very high impedance.

You can never have too much capacitive filtering in a power supply. OK, those audio dudes with the huge capacitors on their car amps- that's too much. :)

Nice! thats the info i was looking for.

once again, thanks to everyone.